kernel: Add /dev/zero

apps/init.cpp

@@ -19,6 +19,7 @@ static void populate_devfs()
 
     xmknod("/dev/console", 0666, 1, 0);
     xmknod("/dev/null", 0666, 2, 0);
+    xmknod("/dev/zero", 0666, 2, 1);
 }
 
 int main()

kernel/CMakeLists.txt

@@ -38,6 +38,7 @@ set(SOURCES
     src/fs/tmpfs/FileSystem.cpp
     src/fs/devices/DeviceRegistry.cpp
     src/fs/devices/NullDevice.cpp
+    src/fs/devices/ZeroDevice.cpp
     src/fs/devices/ConsoleDevice.cpp
     src/InitRD.cpp
     src/ELF.cpp

kernel/src/fs/devices/DeviceRegistry.cpp

@@ -2,6 +2,7 @@
 #include "Log.h"
 #include "fs/devices/ConsoleDevice.h"
 #include "fs/devices/NullDevice.h"
+#include "fs/devices/ZeroDevice.h"
 #include <luna/Vector.h>
 
 struct DeviceDescriptor
@@ -42,6 +43,7 @@ namespace DeviceRegistry
     {
         // Hardcode default devices.
         TRY(register_special_device(DeviceMajorTypes::Memory, 0, NullDevice::create));
+        TRY(register_special_device(DeviceMajorTypes::Memory, 1, ZeroDevice::create));
         TRY(register_special_device(DeviceMajorTypes::Console, 0, ConsoleDevice::create));
 
         return {};

kernel/src/fs/devices/ZeroDevice.cpp

@@ -0,0 +1,6 @@
+#include "fs/devices/ZeroDevice.h"
+
+Result<SharedPtr<Device>> ZeroDevice::create()
+{
+    return (SharedPtr<Device>)TRY(make_shared<ZeroDevice>());
+}

kernel/src/fs/devices/ZeroDevice.h

@@ -0,0 +1,28 @@
+#pragma once
+#include "fs/devices/DeviceRegistry.h"
+
+class ZeroDevice : public Device
+{
+  public:
+    // Initializer for DeviceRegistry.
+    static Result<SharedPtr<Device>> create();
+
+    Result<usize> read(u8* buf, usize, usize length) const override
+    {
+        __builtin_memset(buf, 0, length);
+
+        return length;
+    }
+
+    Result<usize> write(const u8*, usize, usize) override
+    {
+        return 0;
+    }
+
+    bool blocking() const override
+    {
+        return false;
+    }
+
+    virtual ~ZeroDevice() = default;
+};